This invention relates to a system for controlling a semiconductor such as a CCD, and more particularly to an improvement of a construction for connecting an instrument having a semiconductor and a control unit to each other.
Taking, for example, an electronic endoscope system as disclosed in Japanese Laid-Open Patent Application No. Sho 59-70382, this system comprises an endoscope, a control unit connected to this endoscope, and a monitor television connected to this control unit. In operation, this endoscope is inserted into a patient's body and his/her body cavity is observed while watching the monitor television.
The endoscope includes a body, an insert portion extending from the body, a CCD (semiconductor) acting as an image pick-up element, which is mounted on a distal end of the insert portion, and a cable extending backwardly from the body. A first connector is mounted on a distal end of the cable. This first connector is connected to the CCD through electric wires passing through the cable, the body and the insertion portion.
The control unit contains therein a power source circuit for converting an AC voltage to a DC voltage, a control circuit which receives the DC voltage from the power source circuit, and a power source switch interposed between the power source circuit and the control circuit. The operating portion of the power source switch is mounted on a front wall of a housing of the control unit. A second connector is mounted on the front wall of the housing and connected to the control circuit.
The first connector of the endoscope is removably connected to the second connector of the control unit. By this, the control circuit and the CCD are connected to each other.
Incidentally, the CCD, like other semiconductors, has a possibility of suffering from a latch-up phenomenon. This latch-up occurs when a signal terminal is received in the state where no voltage is supplied to a power source terminal of the semiconductor. This results in breakage of the CCD.
In order to prevent this latch-up, the above-mentioned control circuit controls the semiconductor in the following manner. When the power source switch is turned on and the control circuit is connected to the power source circuit, the control circuit outputs a control signal to the signal terminal after it supplies the voltage to the power source terminal of the semiconductor. On the other hand, when the control circuit is disconnected from the power source circuit by turning off the power source switch, the supply of voltage to the power source terminal is stopped after the output of the control signal to the signal terminal has been stopped.
In the case where the first and second connectors are connected to each other in the OFF-state of the power source switch, and thereafter, the power source switch is turned on, the control circuit exhibits a latch-up preventive function. Therefore, a possible breakage of the CCD can be positively prevented. Also, in the case where the power source switch is turned off first and then the connecting state between the first and second connectors is removed, the control circuit exhibits the latch-up preventive function. Therefore, breakage of the CCD can be positively prevented.
However, in the case where the first and second connectors are connected to each other after the power source switch is turned on, the latch preventive function by the control circuit does not work any more. In addition, since the contact elements of the first and second connectors for transmitting control signals are often contacted immediately before the contact elements for supplying voltage to the power source terminal of the CCD are contacted to each other at the starting time of the connecting operation, the CCD receives the control signal before it receives the supply of voltage to the power source terminal. As a result, the CCD is broken by latch-up. Similarly, in the case where the connection between the first and second connectors is removed in the state where the power source switch is in the ON-state, there is still a possibility that the CCD is broken by latch-up.
In order to prevent the latch-up, it was a conventional practice to request the user to turn on the power source switch after the connector devices are connected and then remove the connection between the first connector and the second connector after the power source switch is turned off.
However, since this on/off operation of the power source switch and the sequential order of connection of the connectors are left to the user's manual operation, the CCD is frequently subjected to a failure by the user who inadvertently connects the connectors in wrong order.